SPOT WELDING

Write the definition of welding

Spot welding is a pressure resistance welding in which overlapping sheets are joined by local fusion at one or more spots. Heat is produced by electrodes placed above and below the workpiece.

Write the principle of resistance welding.i.e. heat is generated because of resistance to the flow of elect current through the workpiece.

PROCEDURE:
1. Job should be cleaned from grease, dirt, paint, scale, rust, oxides etc.
2. The tip of electrodes must be cleaned by emery paper regularly.
3. To avoid the electrodes getting overheated, water is kept running for cooling.
4. Proper welding current is to be set on current selector switch.
5. Proper time has to be set on timer.
6. Electrodes are brought against the overlapping surfaces of workpiece and small pressure is applied for just physical contact.
7. Welding current is switched on for proper time.
8. As current passes, a small spot area is heated and weld takes place. TEMP is about 815 to 930 degree centigrade.
9. Now current is cut off and extra force/ pressure is applied to electrodes' tips. Hold until the metal cools down and gains strength.
10. After that electrode pressure is released to remove the spot welded piece.

Draw figure and write advantages & disadvantages.
Write application/ uses of spot welding.